Semiconductor device having a ball grid array and method therefor

ABSTRACT

A semiconductor device ( 50 ) includes a semiconductor die ( 52 ) having electronic circuitry that is connected to a substrate ( 54 ). The substrate ( 54 ) is used to interface the semiconductor die ( 52 ) to a printed circuit board ( 64 ). The substrate ( 54 ) includes a plurality of bonding pads ( 56, 58 ). A first portion of the plurality of bonding pads are soldermask defined (SMD) bonding pads ( 56 ) and a second portion of the plurality of bonding pads are non-soldermask defined (NSMD) bonding pads ( 58 ). Using a combination of SMD and NSMD bonding pads provides the advantages of good thermal cycling reliability and good bending reliability over devices that have only SMD bonding pads or NSMD bonding pads.

FIELD OF THE INVENTION

[0001] This invention relates generally to semiconductor devices, andmore particularly, to a semiconductor device having a ball grid arrayand method therefor.

BACKGROUND OF THE INVENTION

[0002] In some semiconductor manufacturing processes, such as forexample, “flip chip”, bumps are fabricated on pad areas of asemiconductor die in order to interconnect the die to a package or to asubstrate. The substrate is used to interface the electrical circuits ofthe semiconductor die to a printed circuit board. In some instances, thesemiconductor die may be attached directly to the printed circuit board.

[0003] An integrated circuit manufactured using “flip chip” technologymay have hundreds of these solder bumps. In solder ball, or solder bump,technology, various techniques may be used to define the area on thepads for receiving the solder balls. One technique provides a solderball connection area called a soldermask defined (SMD) bonding pad.Another technique provides a solder ball connection area known as anon-soldermask defined (NSMD) bonding pad.

[0004]FIG. 1 illustrates a soldermask defined bonding pad in accordancewith the prior art. A SMD bonding pad is provided on both a substrate 12and on a printed circuit board 22. The SMD bonding pad on substrate 12includes a metal bonding pad 14 formed on substrate 12. Substrate 12 isgenerally used to interconnect, or interface a semiconductor die (notshown) with printed circuit board 22. A soldermask coating 16 is formedover substrate 12 and covers a portion of bonding pad 14. A portion ofthe metal bonding pad 14 is left exposed. A solder ball 24 is thenattached to bonding pad 14. When connecting substrate 12 to printedcircuit board 22, a bonding pad 20 is formed on the surface of printedcircuit board 22. A solder mask 18 is formed over the surface of printedcircuit board 22 and overlaps a portion of bonding pad 20 to formanother SMD bonding pad. The openings in the soldermask coatings 16 and18 define the area of the bonding pads to which the solder attaches formaking electrical contact between the substrate 12 and printed circuitboard 22. Also, the soldermask prevents liquid solder from flowing overareas where it is not wanted, such as for example, along a metal trace.In addition, the soldermask functions to shape the solder ball 24 afterit is reflowed.

[0005]FIG. 2 illustrates a non-soldermask defined bonding pad inaccordance with the prior art. An NSMD bonding pad is illustrated onboth a substrate 32 and a printed circuit board 42. The NSMD bonding padon substrate 32 includes a metal bonding pad 34. As described above inconnection with FIG. 1, substrate 32 is used to interconnect, orinterface a semiconductor die (not shown) with printed circuit board 42.A soldermask coating 36 is formed over substrate 32 and has an openingthat does not typically contact or overlap bonding pad 34. A solder ball44 is attached to bonding pad 34. Likewise, a bonding pad 40 is formedon the surface of printed circuit board 42 where it is intended toconnect to bonding pad 34. A solder mask 38 is formed over the surfaceof printed circuit board 42 and has openings that do not typically coveror overlap any of bonding pad 40. The shape and size of the bonding padsfunction to determine the shape of the solder ball after solder reflow.

[0006] SMD bonding pads are known to provide greater reliability inapplications where the printed circuit board is subjected to highbending loads, such as for example, a cellular telephone that includespush buttons on the same printed circuit board as the integratedcircuits. However, SMD bonding pads are not known for providing highreliability in those applications that subject the printed circuit boardto thermal cycling, such as for example, in an automotive application.In contrast, NSMD bonding pads are known to provide high reliability inextreme temperature applications, but not high reliability whensubjected to bending loads.

[0007] Therefore, a need exists for a technique to attach asemiconductor device to a printed circuit board that provides improvedbending reliability as well as improved reliability when exposed totemperature cycling.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention is illustrated by way of example and notlimited in the accompanying figures, in which like references indicatesimilar elements, and in which:

[0009]FIG. 1 illustrates a soldermask defined bonding pad in accordancewith the prior art.

[0010]FIG. 2 illustrates a non-soldermask defined bonding pad inaccordance with the prior art.

[0011]FIG. 3 illustrates a cross-sectional view of a semiconductordevice and printed circuit board in accordance with an embodiment of thepresent invention.

[0012]FIG. 4 illustrates a bottom-up view of a portion of thesemiconductor device of FIG. 3.

DESCRIPTION OF A PREFERRED EMBODIMENT

[0013] Generally, the present invention provides a semiconductor deviceand a method for attaching the semiconductor device to a printed circuitboard. The semiconductor device includes a semiconductor die havingelectronic circuitry that is connected to a substrate. The substrate isused to interface the semiconductor die to a printed circuit board. Thesubstrate includes a plurality of bonding pads arranged as a grid array,for example, Land, Ball, and Column. A first portion of the plurality ofbonding pads are characterized as soldermask defined (SMD) bonding padsand a second portion of the plurality of bonding pads are characterizedas non-soldermask defined (NSMD) bonding pads. It has been determinedthat the advantages of good thermal cycling reliability and good bendingreliability can be achieved for the same printed circuit board byincluding both SMD and NSMD bonding pads on the same semiconductordevice.

[0014]FIG. 3 illustrates a cross-sectional view of a semiconductordevice 50 and printed circuit board 64 in accordance with an embodimentof the present invention. Semiconductor device 50 includes asemiconductor die 52 that is attached to a substrate 54. In theillustrated embodiment, semiconductor die 52 is an integrated circuitfabricated from a silicon wafer. Substrate 54 is a commonly usedsubstrate for interfacing the semiconductor die 52 with a printedcircuit board and is typically formed from an organic material.Semiconductor die 52 is attached to substrate 54 using one of thecommonly known techniques, such as for example, the C4 (ControlledCollapse Chip Connection) bump process, the E3 (Extended EutecticEvaporative) bump process, the conductive adhesive process, or the wirebond process. The method used to connect semiconductor die 52 tosubstrate 54 is not important for purposes of describing the presentinvention and will not be described further. After semiconductor die 52is attached to the substrate 54, the surface of the substrate and thedie are encapsulated using a common mold compound encapsulationmaterial.

[0015] SMD bonding pads 56 and NSMD bonding pads 58 are formed on theother side of substrate 54. The bonding pads are typically laid out asan array, or matrix, for electrically connecting the substrate to theprinted circuit board. An SMD bonding pad 56 includes a metal bondingpad, typically made from copper. An insulative coating 62, also known asa soldermask, is deposited on substrate 54 so that an opening is formedover bonding pad 56. The opening is smaller than the bonding pad andoverlaps a portion of bonding pad 56. The overlapping portion ofsoldermask 62 is for defining a connection area for a solderinterconnect and shapes the solder connection between the substrate andthe printed circuit board.

[0016] NSMD bonding pads 58 include metal bonding pads 58. The bondingpads are not covered with soldermask 62 and have an exposed edge. In theNSMD bonding pad technique, the exposed edge of the bonding pad definesa connection area for a solder interconnect.

[0017] In the illustrated embodiment, printed circuit board 64 has acombination of SMD and NSMD bonding pads in locations that correspond tothe bonding pads of semiconductor device 50. As described above, SMDbonding pads 66 are formed by overlapping a portion of the metal bondingpads with soldermask 70 so that the edge of the soldermask openingsdefine the solder ball shape. Also, NSMD bonding pads 68 are formed bymaking the soldermask openings large enough that the metal bonding padsare not covered.

[0018] Solder balls (not shown in FIG. 3) are formed on bonding pads 56and 58. To connect semiconductor device 50 to printed circuit board 64,the solder balls are remelted, or reflow attached, after placing thesolder balls of semiconductor device 50 in contact with the bonding padsof printed circuit board 64.

[0019] Through experimentation, it has been determined that the bestbending reliability and the best thermal cycling reliability is achievedby using a combination of both SMD and NSMD bonding pad types to connecta substrate to a printed circuit board as illustrated in FIG. 3. In theillustrated embodiment, SMD bonding pads are used around the outer edgeof the substrate because these are the pad locations that have beenfound to be more likely to break when subjected to bending stress.Likewise, NSMD bonding pads are used for the interior locations of thesubstrate, as illustrated in FIG. 3, because these are the pad locationsmore likely to fail under thermal cycling. Note that in the illustratedembodiment, the outer three rows of bonding pads are SMD, but in otherembodiments, a different number of outer rows may be SMD. Also, theactual locations for the SMD and NSMD bonding pads may be differentdepending on a number of variables such as die size, number of bondingpads, solder ball volume, substrate thickness, encapsulation thickness,etc. Also, in other embodiments, a different combination of SMD and NSMDbonding pads may be used to provide improved thermal cycling and bendingreliability. As an example, a combination of SMD and NSMD bonding padsmay be used on the substrate, while the printed circuit board has oneonly one of either SMD or NSMD bonding pads. In addition, in anotherembodiment, the SMD and NSMD combination may be used on the printedcircuit board but not on the substrate and still be within the scope ofthe invention.

[0020]FIG. 4 illustrates a bottom-up view of a portion 80 ofsemiconductor device 50 of FIG. 3. The cross-hatching over portion 80 issoldermask 62. The left side of portion 80 is an edge of substrate 54.As can be seen in FIG. 4, SMD bonding pads 56 are formed by makingopenings in soldermask 62 that are smaller than the metal bonding pads.As discussed above, the shape of the solder ball after melting andconnecting to the printed circuit board is largely determined bysoldermask 62. The NSMD bonding pads 58 are formed by making openings insoldermask 62 that are larger than the bonding pad. The shape of thesolder connection is determined by the edge of the metal pad and not bythe soldermask. Note that in the illustrated embodiment, the metal padsof NSMD bonding pads 58 are slightly larger than the metal pads of SMDbonding pads 56. Also, note that for illustration purposes, traces areprovided between adjacent bonding pads. In other embodiments, therouting of traces and the presence of vias (not shown) is determined bythe particular application.

[0021] While the invention has been described in the context of apreferred embodiment, it will be apparent to those skilled in the artthat the present invention may be modified in numerous ways and mayassume many embodiments other than that specifically set out anddescribed above. For example, in the illustrated embodiment, the bondingpads have a circular shape. In other embodiments, the bonding pads mayhave a square, rectangular, or other shape. Accordingly, it is intendedby the appended claims to cover all modifications of the invention whichfall within the true scope of the invention.

What is claimed is:
 1. A semiconductor device, comprising: asemiconductor die having electronic circuitry; and a substrate forinterfacing the semiconductor die to a printed circuit board, thesubstrate having a plurality of bonding pads for connecting to theprinted circuit board, a first portion of the plurality of bonding padsbeing characterized as soldermask defined bonding pads and a secondportion of the plurality of bonding pads being characterized asnon-soldermask defined bonding pads.
 2. The semiconductor device ofclaim 1, wherein a soldermask defined bonding pad on a surface of thesubstrate comprises a metal bonding pad and having an insulative coatingon the substrate overlapping a portion of the metal bonding pad, theoverlapping portion for defining a connection area for a solderinterconnect.
 3. The semiconductor device of claim 1, wherein anon-soldermask defined bonding pad on a surface of the substratecomprises a metal bonding pad and having an exposed edge, the exposededge defining a connection area for a solder interconnect.
 4. Thesemiconductor device of claim 1, wherein the first portion of theplurality of bonding pads are the outermost bonding pads in an array ofbonding pads.
 5. The semiconductor device of claim 4, wherein theoutermost bonding pads are the three outer rows of bonding pads on thesubstrate.
 6. The semiconductor device of claim 4, wherein the secondportion of the plurality of bonding pads are the innermost bonding padsin the array of bonding pads.
 7. The semiconductor device of claim 1,further comprising a printed circuit board for receiving thesemiconductor die, the printed circuit board having a plurality ofbonding pads for connecting to the substrate, a first portion of theplurality of bonding pads being characterized as the soldermask definedbonding pads and a second portion of the plurality of bonding pads beingcharacterized as the non-soldermask defined bonding pads.
 8. Thesemiconductor device of claim 1, further comprising a printed circuitboard for receiving the semiconductor die, the printed circuit boardhaving a plurality of bonding pads for connecting to the substrate, theplurality of bonding pads being characterized as soldermask definedbonding pads.
 9. The semiconductor device of claim 1, further comprisinga printed circuit board for receiving the semiconductor die, the printedcircuit board having a plurality of bonding pads for connecting to thesubstrate, the plurality of bonding pads being characterized asnon-soldermask defined bonding pads.
 10. A printed circuit board,comprising a plurality of bonding pads for connecting to a semiconductordevice, a first portion of the plurality of bonding pads beingcharacterized as soldermask defined bonding pads and a second portion ofthe plurality of bonding pads being characterized as non-soldermaskdefined bonding pads.
 11. The printed circuit board of claim 10, whereinthe printed circuit board is a substrate for interfacing a semiconductordie to the printed circuit board.
 12. The printed circuit board of claim10, wherein the first portion of the plurality of bonding pads are theoutermost bonding pads in an array of bonding pads.
 13. The printedcircuit board of claim 10, wherein the outermost bonding pads are thethree outer rows of bonding pads of the printed circuit board.
 14. Theprinted circuit board of claim 10, further comprising a substrate, thesubstrate for interfacing the printed circuit board to a semiconductordie, a first portion of a plurality of bonding pads on the substratebeing characterized as the soldermask defined bonding pads and a secondportion of the plurality of bonding pads being characterized as thenon-soldermask defined bonding pads.
 15. The printed circuit board ofclaim 10, further comprising a substrate, the substrate for interfacingthe printed circuit board to a semiconductor die, the substrate having aplurality of bonding pads for connecting to the printed circuit board,the plurality of bonding pads being characterized as soldermask definedbonding pads.
 16. The printed circuit board of claim 10, furthercomprising a substrate, the substrate for interfacing the printedcircuit board to a semiconductor die, the substrate having a pluralityof bonding pads for connecting to the printed circuit board, theplurality of bonding pads being characterized as non-soldermask definedbonding pads.
 17. A method for attaching a semiconductor device to aprinted circuit board, the semiconductor device comprising asemiconductor die connected to a substrate, the method comprising thesteps of: providing a plurality of bonding pads on a surface of thesubstrate for electrically connecting the substrate to the printedcircuit board; and depositing a soldermask over the surface of thesubstrate to define a first portion of the plurality of bonding pads assoldermask defined bonding pads and to define a second portion of theplurality of bonding pads as non-soldermask defined bonding pads. 18.The method of claim 17, further comprising a step of forming solderballs on the plurality of bonding pads.
 19. The method of claim 18,further comprising the steps of: providing a plurality of bonding padson the surface of the printed circuit board for electrically connectingto the plurality of bonding pads on the substrate; and depositing asoldermask over the surface of the printed circuit board to define afirst portion of the plurality of bonding pads on the printed circuitboard as soldermask defined bonding pads and to define a second portionof the plurality of bonding pads on the printed circuit board asnon-soldermask defined bonding pads.
 20. A method for attaching asemiconductor device to a printed circuit board, the semiconductordevice comprising a semiconductor die connected to a substrate, themethod comprising the steps of: providing a plurality of bonding pads ona surface of the printed circuit board for electrically connecting theprinted circuit board to the substrate; and depositing a soldermask overthe surface of the printed circuit board to define a first portion ofthe plurality of bonding pads as soldermask defined bonding pads and todefine a second portion of the plurality of bonding pads asnon-soldermask defined bonding pads.